The present invention generally relates to switched supplies systems and, more particularly, to line driver technology for xDSL communication.
With advancements in technology, the transmission of voice and data at faster rates and in larger volumes is always in demand. One solution to fulfilling these demands is digital subscriber line (DSL) technology. DSL technology has been introduced into the field of broadband networking, among other reasons, to overcome issues faced by traditional voice band technology. Such issues include, but are not limited to, bandwidth limitations. Multiple DSL technologies exist including, but not limited to, rate adaptive DSL (RADSL), symmetric DSL (SDSL), multi-rate SDSL (M/SDSL), high bit-rate DSL (HDSL), very high bit-rate DSL (VDSL), and asymmetric DSL (ADSL).
ADSL technology utilizes the infrastructure already in place in a public switched telephone network (PSTN), including copper loops, constructed of copper wires, between a customer premise and a central office. Advantageously, ADSL technology does not require replacement of network equipment such as routers, switches, firewalls and Web servers, which are commonly used in today""s paradigm for broadband access.
A DSL modem provides communication capabilities for the transmission and receipt of information utilizing ADSL technology. Typically, discrete multi-tone (DMT) line coding is utilized by the DSL modem for the transmission of DMT symbols from a source to a destination.
Due to its Gaussian-like distribution, DMT signals are characterized by a very high peak to RMS ratio (PAR), also known as crest factor, which is typically around 15 dB. Occasionally, high-peak signals are transmitted. Generally, a high crest factor indicates that a signal has rare, but large, deviations from its normal levels, while a smaller crest factor indicates the easier it is to manipulate and transmit the signal. One of the problems of high crest factor signals is high-power consumption by the modem, specifically, by a line driver located within the modem, that is caused by high voltage supply rails required to accommodate the large and rare signal peaks.
To improve power consumption levels of line drivers for high crest factor signals, which occur at different times during the transmission of DMT symbols, a multi-level power supply, or line driver, is typically utilized (i.e., Class G line driver). The multi-level line driver comprises a high-power supply rail and a low-power supply rail. For transmission of signals having a typical level, the line driver output signal is bounded by the low-power supply rail. However, when an indication of a high crest factor signal is received, the line driver, having a multi-level power supply, switches to the high-power supply rail to accommodate for the high crest factor signal. Switching between high and low-power supply rails is performed when a signal crosses a predetermined voltage level. In this context, the term crest factor signal is defined to describe a segment of the signal in which the signal had a peak voltage level higher then the predetermined voltage level. At the present time, Class-G line drivers are implemented by using between three to four external power supplies. The power supplies used are usually of the switch mode type to improve efficiency. The required power supplies are separate from the Class-G line driver, and therefore require additional board space and cost. To that, since the required voltages are produced separate from the line drivers, there is no direct control of these voltages in the design and/or fabrication of the line drivers themselves, and so the line driver engineers do not have the opportunity to optimize the efficiency. Therefore, a system and method for traversing the need for multiple external power supplies is desired.
In light of the foregoing, a line driver is disclosed. Generally, the structure of the line driver contains an amplifier stage that can operate at various voltage levels. The first external supply voltage is connected to a first power supply input of the amplifier stage. The line driver also includes a charge pump that generates at least a first internal supply voltage supplied to the amplifier stage. A switch control circuit is also included within the line driver to regulate the voltage output from the charge pump.
The present invention can also be viewed as a method for supplying various voltages to a load. In this regard, the method can be broadly summarized by the following steps: generating an internal supply voltage from an external supply voltage, wherein the internal supply voltage is less than the external supply voltage; supplying the first internal supply voltage to the load; and regulating the generation and supply of the first internal supply voltage.
Other systems and methods of the present invention will be or become apparent to one with skill in the art upon examination of the following drawings and detailed description. It is intended that all such additional systems, methods, features, and advantages be included within this description, be within the scope of the present invention, and be protected by the accompanying claims.